1. Field of the Invention
The invention relates to a DC-DC converter more especially of the voltage booster type.
2. Description of the Prior Art
To raise or lower a DC voltage there are usually provided: a single chopping switch for transforming this DC voltage into a periodic voltage, a transformer which boosts or lowers the voltage thus chopped and which isolates the output from the input, as well as a rectifier for converting into a DC voltage the periodic voltage supplied by the secondary of the transformer. In addition, such converters generally comprise an input filter, for example of the LC type, for avoiding reinjection of the chopped current into the power supply source as well as an output filter, for example also of the LC type, for smoothing the rectified current.
In the converters of this type known up to now, the switch is in series with the primary winding of the transformer and at the terminals of this series assembly is disposed in parallel a capacitor which receives the input DC voltage. In a circuit called "direct" or "forward", the secondary winding of the transformer is in the same direction as the primary winding and the energy is transmitted into the secondary circuit only during the conducting phases of the switch. In a so-called "recovery", or "restoration" or "fly-back" converter, the secondary winding of the transformer is in the opposite direction to the primary winding and the secondary circuit only produces energy during the disabled phases of the switch.
The secondary winding of the transformer in these circuits comprises a large number of turns for, since the energy is only transmitted to the secondary circuit during the fraction of the period of the chopped signal, the voltage at the terminals of the secondary must be higher than the output voltage. Furthermore, because of their high number, the turns are wound in several layers which create therebetween parasite capacities which cause energy losses which are a function of the square of the voltage. Thus it is very difficult to construct a converter having a good efficiency at a high output voltage, for example of the order of a kilovolt.
The invention overcomes these drawbacks.